Color-insensitive window coatings for ambient light sensors

Abstract

An electronic device may have a display with a transparent layer such as a cover layer. An ambient light sensor may be aligned with an ambient light sensor window formed from an opening in a masking layer on the transparent layer in an inactive portion of the display. To help mask the ambient light sensor window from view, the ambient light sensor window may be provided with a black coating that matches the appearance of surrounding masking layer material while allowing light to reach the ambient light sensor. The black coating may include multiple pigments and may have a flat spectrum to enhance color ambient light measurements made with the ambient light sensor. The black coating may include a polymer binder or other binder that contains multiple pigments. The pigments may include a black pigment, a blue pigment, and an infrared-light-transparent pigment and/or other pigments.

What is claimed is: 
     
       1. An electronic device, comprising:
 a light sensor; 
 a transparent structure having a portion forming a window that is aligned with the light sensor; and 
 a coating on the transparent structure, wherein the coating is interposed between the light sensor and the transparent structure, wherein the coating overlaps the window and the light sensor, the coating has a first transmission at red wavelengths and a second transmission at blue wavelengths, the first and second transmissions are transmitted through the window and the coating, the first transmission is greater than the second transmission, the first transmission is less than 4/3 of the second transmission, and the coating transmits less than 30% of light across visible light wavelengths. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the light sensor comprises an ambient light sensor. 
     
     
       3. The electronic device defined in  claim 2  further comprising a display, wherein the transparent structure comprises a transparent layer of the display. 
     
     
       4. The electronic device defined in  claim 3  wherein the coating includes at least three pigments. 
     
     
       5. The electronic device defined in  claim 4  wherein the pigments include black pigment. 
     
     
       6. The electronic device defined in  claim 5  wherein the pigments include a pigment selected from the group consisting of: blue pigment and infrared-transparent pigment. 
     
     
       7. The electronic device defined in  claim 5  wherein the pigments include blue pigment. 
     
     
       8. The electronic device defined in  claim 7  wherein the pigments include infrared-transparent pigment. 
     
     
       9. The electronic device defined in  claim 8  wherein the ambient light sensor comprises a color ambient light sensor. 
     
     
       10. The electronic device defined in  claim 5  wherein the ambient light sensor comprises a color ambient light sensor. 
     
     
       11. The electronic device defined in  claim 5  wherein the coating has a thickness of 3-8 microns and wherein the black pigment comprises carbon black with an aggregate size of less than 20 microns and a particle size of less than 30 nm. 
     
     
       12. An electronic device, comprising:
 a display having a display cover layer that overlaps an active area with pixels that display images and an inactive area without pixels; 
 an ambient light sensor that receives light through a continuous window in a portion of the display cover layer that overlaps the inactive area, wherein the continuous window overlaps the ambient light sensor; and 
 a coating on the coutinuous window of the display cover layer, wherein the coating includes at least three pigments and wherein the coating and the at least three pigments are in the continuous window and directly overlap the ambient light sensor. 
 
     
     
       13. The electronic device defined in  claim 12  wherein the coating includes black pigment. 
     
     
       14. The electronic device defined in  claim 13  wherein the black pigment comprises carbon black. 
     
     
       15. The electronic device defined in  claim 14  wherein the carbon black has an aggregate size of less than 15 microns and a particle size of less than 25 nm. 
     
     
       16. The electronic device defined in  claim 15  wherein the coating is interposed between the ambient light sensor and the display cover layer and wherein the ambient light sensor comprises a color ambient light sensor. 
     
     
       17. The electronic device defined in  claim 16  wherein the coating has a first transmission at red wavelengths and a second transmission at blue wavelengths, wherein the first transmission is less than 4/3 of the second transmission, and wherein the first transmission and the second transmission have transmission values of 1-10%. 
     
     
       18. An electronic device, comprising:
 a housing; 
 a display in the housing that has a transparent layer; 
 a black opaque masking layer on the transparent layer that has an opening that forms an ambient light sensor window; 
 a color ambient light sensor in the housing that receives ambient light through the ambient light sensor window; and 
 a layer on the transparent layer in the opening that has a total light transmission at 500 nm and that has a total light transmission at 600 nm that is less than 4/3 of the total light transmission at 500 nm, wherein the total light transmission at 500 nm and the total light transmission at 600 nm have transmission values between 1% and 10% through the layer in the opening, wherein the layer comprises at least three different pigments, and wherein the three pigments include black pigment and blue pigment. 
 
     
     
       19. The electronic device defined in  claim 18  wherein the at least three different pigments are in the opening in the black opaque masking layer. 
     
     
       20. The electronic device defined in  claim 18  wherein the three pigments further include infrared-transparent pigment and wherein the layer includes polymer binder. 
     
     
       21. The electronic device defined in  claim 20  wherein the at least three different pigments directly overlap the ambient light sensor window and the color ambient light sensor.